کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
1331452 | 979005 | 2007 | 10 صفحه PDF | دانلود رایگان |
![عکس صفحه اول مقاله: Crystal structures and dielectric properties of ordered double perovskites containing Mg2+ and Ta5+ Crystal structures and dielectric properties of ordered double perovskites containing Mg2+ and Ta5+](/preview/png/1331452.png)
The ordered double perovskites ALaMgTaO6 (A=Ba, Sr, Ca) and La2Mg(Mg1/3Ta2/3)O6 have been prepared and characterized. Synchrotron X-ray powder diffraction analyses show that all four compounds exhibit a rock-salt type ordering of the B-site cations (Mg2+/Ta5+) and a random distribution of A-site cations (A2+/La3+). The space group symmetries are determined to be Fm3¯m for BaLaMgTaO6, and P21/n for SrLaMgTaO6, CaLaMgTaO6, and La2Mg(Mg1/3Ta2/3)O6. Diffuse-reflectance spectroscopy shows these ordered perovskites have optical band gaps in the range of 4.6−4.8 eV. These values are roughly 1 eV wider than the ternary perovskite oxides of Ta5+ such as KTaO3, due to narrowing of the conduction bandwidth which results from Mg2+/Ta5+ ordering. These compounds are insulators with dielectric permittivities of κ=18–23, dielectric losses of tan δ=0.004–0.007, and small temperature coefficients of capacitance <100 ppm/K over the temperature range 20–150 °C. BaLaMgTaO6 is of particular interest because it possesses a near-zero temperature dependence of capacitance.
XRPD patterns at low angle range for the Mg/Ta complex perovskite oxides, showing various origins of diffraction planes: s—rock-salt type cation ordering, h—1:2 cation ordering, p—primitive cube edge, and d—octahedral tilting.Figure optionsDownload as PowerPoint slide
Journal: Journal of Solid State Chemistry - Volume 180, Issue 10, October 2007, Pages 2798–2807